Hot or cold, the coral can't win

CORAL reefs can be bleached when water gets colder as well as when it gets warmer. This means that corals could be in trouble whichever way climate change affects local sea temperature.

Bleaching occurs when corals become stressed, causing them to expel the symbiotic algae they depend on for most of their food. And because warmer than usual temperatures stress corals, global warming is already recognised as a threat to reefs. Now Australian researchers Ove Hoegh-Guldberg and Maoz Fine at the University of Queensland in Brisbane have documented a mass bleaching triggered by cold temperatures. Last June, high winds and low humidity at the southern end of the Great Barrier Reef off the Queensland coast caused temperatures to drop as low as 12 °C, and by the following month widespread bleaching could be seen in shallow-water coral (Coral Reefs, vol 23, p 444)

The researchers say that high-latitude reefs may ...

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